L. Lottermoser

Solution of Ge(111)-(4 × 4)-Ag structure using direct methods applied to X-ray diffraction data

Abstract A structure model for the Ge(111)-(4×4)-Ag surface is proposed. The model was derived by applying direct methods to surface X-ray diffraction data. It is a missing top layer reconstruction with six Ag atoms placed on Ge substitutional sites in one triangular subunit of the surface unit cell. A ring-like assembly containing nine Ge atoms is found in the other triangular subunit. The stability of the ring assembly may be due to Ge–Ge double bond formation. Trimers of Ge atoms, similar to the trimers found on the Ge (111)-( 3 × 3 ) R 30°- Ag surface, are placed in the corners of the unit cell.

Structure determination of the indium-induced Ge(103)-(1×1) reconstruction by surface X-ray diffraction

Abstract A detailed structural model of the indium-induced Ge(103)-(1×1) surface reconstruction has been established by analyzing an extensive set of X-ray data recorded with synchrotron radiation. Our results show that models with one indium and one germanium adatom per unit cell are incompatible with the data. A model with two indium adatoms per unit cell saturates all the dangling bonds on the Ge(103) surface, preserves the symmetry and is compatible with all of the experimental results.

The atomic structure of the Si(111) reconstruction

Abstract We have studied the atomic structure of the (2 3 ×2 3 ) R °- Sn reconstruction induced by adsorption of about 1.1 monolayers of Sn on Si(111) using surface X-ray diffraction (SXRD) and scanning tunnelling microscopy (STM). The experimentally obtained structure factors in SXRD are in contradiction with existing models in the literature and we conclude the need for a new surface atomic structure model. We have been able to determine a number of properties of an appropriate surface model to allow a better fit to the experimental structure factors.

Bismuth on copper (110): analysis of the c(2 × 2) and p(4 × 1) structures by surface X-ray diffraction

Abstract Surface X-ray diffraction has been used to analyze the atomic structures of the Cu(110)-c(2 × 2)Bi and Cu(110)-p(4 × 1)Bi reconstructions with submonolayer coverages. A quasi-hexagonal c(2 × 2) adlayer structure is formed when half a monolayer of bismuth is deposited; the coverage corresponds to 1.08 × 10 −15 atoms cm −2 . There is one Bi atom per c(2 × 2) surface unit cell, and the nearest-neighbor distance on the planar overlayer was found to be 4.43 A. In the case of the p(4 × 1) reconstruction formed at a coverage of 0.75 monolayers, both the in-plane and out-of-plane data are in excellent agreement with a model in which every fourth Cu row in the [001] direction of the topmost layer is replaced by Bi atoms to form a substitutional surface alloy.

Growth morphology and structure of bismuth thin films on GaSb(110)

Abstract Photoelectron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy and surface X-ray diffraction were used to investigate the growth of thin layers of bismuth on GaSb(110). At submonolayer coverages, growth of two-dimensional islands occurs. A uniform (1×1)-reconstruction is formed at a coverage of one monolayer. A structural model derived from X-ray diffraction data is presented for this phase. The (1×1)-phase consists of zigzag chains of bismuth atoms bonded alternately to the surface cations and anions of the bulk-terminated unrelaxed (110) surface. We propose that the (1×1)-phases formed by antimony and bismuth adsorbates on (110) surfaces of other III–V compound semiconductors are also described by the epitaxial continued layer model.

Atomic structure of a stable high-index Ge surface: Ge(103)-(4 × 1)

Abstract Based on scanning tunneling microscopy and surface X-ray diffraction, we propose a complex structural model for the Ge(103)-(4 × 1) reconstruction. Each unit cell contains two (103) double steps, which gives rise to the formation of stripes of Ge atoms oriented in the [3¯01] direction. The stripes and the spaces between them are covered with threefold-coordinated Ge adatoms. Charge is transferred from the bulk-like edge atoms of the double steps to the adatoms. The formation of the reconstruction can be explained in terms of stress relief, charge transfer, and minimization of the dangling bonds.

Hut clusters on Ge(001) surfaces studied by STM and synchrotron X-ray diffraction

Abstract Nanoscale hut clusters formed on Ge(001) surfaces by depositing one monolayer of indium and annealing at temperatures between 350 and 500°C were studied by scanning tunnelling microscopy and synchrotron X-ray diffraction. It was found that the hut clusters form regular arrays over the entire surface. The huts are aligned with the 〈100〉 directions of the bulk Ge crystal and bounded by {103} facets. A structural model is proposed in which the clusters consist of Ge atoms and the dangling bonds on the {103} facets are saturated by In atoms which thereby stabilize the structure.

Bismuth on GaSb(110): Structural Determination of the 1×1 and 1×2 Phases by Surface X-Ray Diffraction

The surface geometry of the 1×1 and 1×2 phases of bismuth on GaSb(110) has been determined using surface X-ray diffraction with synchrotron radiation. The bismuth atoms form zigzag chains along the direction of the substrate. For the 1×1 phase four different registries of the bismuth chains with respect to the GaSb(110) substrate are possible. It was found that only the epitaxial continued layer structure was in good agreement with the experimental data. In the 1×2 reconstruction every second zigzag chain in the uppermost substrate layer is missing. The reconstructed surface is terminated with a full monolayer of Bi atoms which also form zigzag chains. The Bi atoms in the chains bond alternately to the first and second layer substrate atoms and the Bi chains are inclined at 34° to the surface. This new structural model explains the higher thermal stability of the 1×2 phase compared to that of the 1×1 phase.